1. Field of the Invention
The present invention relates to a vehicle, and in particular to a vehicle that includes an electrically heated catalyst for purifying exhaust gas of an engine.
2. Description of Related Art
A vehicle has been known that includes an electrically heated catalyst (hereinafter also referred to as an “EHC”) for purifying exhaust gas of an engine. The EHC contains a catalyst and an electric heater for heating the catalyst. It has been known that, performance of the catalyst is degraded when a sulfur content that is contained in the exhaust gas of the engine adheres to the catalyst. A state in which adhesion of the sulfur content causes the reduced performance of the catalyst is referred to as a “sulfur poisoned state”. Once the catalyst is brought into the sulfur poisoned state, purifying performance of the catalyst is degraded, and emissions may consequently be deteriorated. Accordingly, it is desired to eliminate the sulfur poisoned state.
If a temperature of the catalyst is a specified temperature (500° C., for example) or higher, and if a sufficient amount of oxygen (an oxidant) is available, the sulfur content, which is adhered to the catalyst, is oxidized and desorbed from the catalyst. Consequently, the sulfur poisoned state is eliminated.
Japanese Patent Application Publication No. 2012-57576 (JP 2012-57576 A) discloses a technique in which the sulfur poisoned state is efficiently eliminated by supplying electricity to the EHC to increase the temperature of the catalyst and by operating the engine in such a manner that air-fuel ratio of the exhaust gas of the engine becomes leaner (contains more oxygen) than theoretical air-fuel ratio when the catalyst is brought into the sulfur poisoned state.
In recent years, attentions have been paid to a hybrid vehicle in which a built-on battery can be charged by external electric power from an external electric power source (hereinafter referred to as a “plug-in hybrid vehicle”). In the plug-in hybrid vehicle, fuel economy is improved by preferentially consuming the electric power stored in a battery over engine fuel until a remaining capacity of the battery becomes lower than a lower limit (that is, the electric power stored in the battery is used up). Accordingly, opportunities to operate the engine may be much less for the plug-in hybrid than for a normal hybrid vehicle or a vehicle driven by an engine.
As described above, JP 2012-57576 A discloses the technique to efficiently eliminate the sulfur poisoned state of the catalyst by concurrently using electric power supply to the EHC and the exhaust gas of the engine.